plugins.rb

module Plugin1
  hello("hello")
end

module PluginContainer
  def self.included(base)
    base.extend(ClassMethods)
  end
  module ClassMethods
    include Plugin1
  end
end


class Greeter
  def self.hello(name)
    p "hello #{name}"
  end

  include PluginContainer
  
  hello("from greeter")
end

# undefined method `hello' for Plugin1:Module (NoMethodError)